Generally, in a mobile communication system, when a channel is set for a communication, the channel has one or more transmission formats. Since the present invention particularly relates to a case in which the channel has more than one transmission format, explanations are provided for the case in which the channel has more than one transmission format in the following.
In the following, explanations are provided for a transport channel in a WCDMA scheme of 3GPP as the channel.
FIG. 1 shows a mapping relationship among major physical channels (left side), transport channels (center) and logical channels (right side). The transport channel is a channel provided from a physical layer to a MAC sublayer, and it is classified based on transmission forms, and is characterized by information that is transferred via a radio interface and how it is transferred. By the way, DPCH of the physical channel includes DPDCH (Dedicated Physical Data Channel) for transmitting data and DPCCH (Dedicated Physical Control Channel) for transmitting a control command for transmission power control and a pilot bit and the like. By multiplexing a plurality of transport channels into the physical channel and transmitting them, multiplexing of user data and control information, and multiplexing of data of plurality of users due to multiple calls can be performed.
As an example, as to a packet channel (non-patent document 1: 3GPP TS34.108 v4.7.0, 6.10.2.4.1.25.2) of a transmission speed of 64 kbps in a downlink, operation is described for a case in which the transport channel has more than one transmission format.
In the packet channel of the transmission speed of 64 kbps, two transport channels DCH are mapped to a physical channel DPDCH for data communication, and logical channels DTCH and DCCH are mapped to the two transport channels DCH respectively. A set of transport formats (TF) used for the transport channels is called a transport format set (TFS). The TF is a format by which TFS is transmitted, and is a format for supplying a transport block for each TTI (transmission time interval) on the transport channel. The transport block is a basic unit when performing data transfer in the physical layer and the MAC layer. A combination of one or more TFs that can be simultaneously transferred in the physical layer is called a transport format combination (TFC). A set of all TFCs that can be transferred by this physical channel is called a transport format combination set (TFCS). As to the packet channel of the transmission speed of 64 kbps, table 1 shows TFS of DCH on which DTCH is mapped as an example, table 2 shows TFS of DCH on which DCCH is mapped as an example, and table 3 shows TFCS as an example.
TABLE 1TFS of DCH to which DTCH is mapped#TF00 × 336TF11 × 336TF22 × 336TF33 × 336TF44 × 336
TABLE 2TFS of DCH to which DCCH is mapped#TF00 × 148TF11 × 148
TABLE 3TFCSDCH to which DTCHDCH to which DCCH#is mappedis mappedTFC00 × 3360 × 148TFC10 × 3361 × 148TFC21 × 3360 × 148TFC31 × 3361 × 148TFC42 × 3360 × 148TFC52 × 3361 × 148TFC63 × 3360 × 148TFC73 × 3361 × 148TFC84 × 3360 × 148TFC94 × 3361 × 148
In each table, “336” and “148” indicate a size (number of bits) of the transport block of DCH to which DTCH is mapped and a size of transport block of DCH to which DCCH is mapped respectively. In addition, each of the coefficients by which these numbers are multiplied indicates a number of transport blocks.
When a radio control station starts communication using the packet channel of the transmission speed of 64 kbps, the radio control station sets TFS, TFCS, QoS (DCH quality target) of each transport channel and the like to report the setting information to a mobile station and a radio base station. Then, the mobile station and the radio base station perform communication based on the setting information. The radio control station sets TF of each DCH for each TTI (sets TFC from the viewpoint of TFCS) based on a size of data to be transmitted and status of radio environment (congestion status of radio section, transmission power required for satisfying the DCH quality target, for example) and the like. Then, the radio base station performs downlink transmission using the TF (or TFC) set by the radio control station.
For example, when there are both of packet data (DTCH) and control information (DCCH) of logical channels as data to be transmitted, the radio control station may select TFC9 shown in the table 3 as TFC. In addition, when there is only the packet data (DTCH) as data to be transmitted but there is not the control information (DCCH), and when the size of the packet data (DTCH) is one that can be adequately transmitted with a transmission speed of 32 kbps, the radio control station selects TFC4 in the table 3 as TFC. In this case, the DCH to which DCCH is mapped is not transmitted (this state is called DTX). In addition, when neither the packet data (DTCH) nor the control information (DCCH) exists as data to be transmitted, the radio control station selects TFC0 in the table 3 as TFC. In this case, the two DCHes are not transmitted (becomes DTX). That is, DPDCH that is a physical channel is not transmitted.
On the other hand, in order to achieve QoS (DCH quality target) of the transport channel, the mobile station performs inner loop power control based on SIR of a short section and performs outer loop power control based on receive quality (BLER or BER) of a long section. Generally, in the inner loop power control, the mobile station (or base station) measures a receive SIR (Signal to Interference ratio) for example, to report, to the base station (or the mobile station), an “UP” command when the receive SIR is below a target SIR, and to report a “Down” command when the receive SIR is not below the target SIR. The base station (or mobile station) changes the transmission power, by 1 dB for example, according to information indicated by the command. In this transmission power control, SIR in a short period which is 0.667 ms typically is measured. In the outer loop power control, the target SIR is controlled such that a block error rate (BLER) or a bit error rate (BER) becomes a target value. In this transmission power control, SIR in a long period that is 100 ms typically is measured.
When a plurality of transport channels are mapped to a physical channel, the outer loop power control is controlled to satisfy QoS (DCH quality target) of each transport channel. By the way, generally, since rate matching is performed to change the number of bits of a coded data sequence mapped to the physical channel in order to satisfy each QoS (DCH quality target) for the plurality of transport channels, QoS can be satisfied for all of the plurality of transport channels by performing outer loop power control for one of the plurality of transport channels. Also when the rate matching is not adequately performed, the mobile station performs outer loop power control so as to satisfy QoS of all transport channels.
On the other hand, as to each TF of a transport channel, the mobile station performs outer loop power control without distinguishing each TF. That is, in a case of DCH to which DTCH is mapped in the example of the packet channel of the transmission speed of 64 kbps, inner loop power control and outer loop power control are performed without distinguishing each of TF0, TF1, TF2, TF3 and TF4. That is, one transport block in TF1 and four transport blocks in TF4 are treated equally.
Next, a case is described in which one transport channel DCH is mapped to A-DPCH (Associated Dedicated Physical Channel) that is one of a downlink physical channel of high speed downlink packet access (HSDPA), and DCCH is mapped to the DCH. The HSDPA is a transmission scheme for realizing high speed packet transmission in a downlink direction (refer to non-patent documents 2 and 3, for example) in 3GPP. The A-DPCH is a dedicated physical channel transmitted being associated with a shared data channel HS-PDSCH (HS-DSCH as a transport channel) and a shared control channel HS-SCCH in HSDPA. In the downlink of HSDPA, since the packet data (DTCH) is transmitted using HS-PDSCH, only control information (DCCH) is transmitted using A-DPCH.
Table 4 shows TFS of DCH to which DCCH is mapped in A-DPCH (non-patent document 1: 3GPP TS34.108 v5.3.0, 6.10.2.4.1.2.2).
TABLE 4TFS of DCH in A-DPCH#TF01 × 0TF11 × 148
In this example, since the number of the transport channel is one, TFS is the same as TFCS. In this case, when there is control information (DCCH) to be transmitted, the radio control station selects TF1 in the table 4 as a transmission format (TF), and selects TF shown in the table 4 as TF when there is no control information (DCCH) to be transmitted. In DCH of A-DPCH of HSDPA, different from the above-mentioned DCH in the packet of the transmission speed of 64 kbps, one transport block of 0 bit is transmitted instead of DTX when there is no control information (DCCH) to be transmitted. By the way, when the transport block of 0 bit is transmitted, since CRC is added to the transport block of 0 bit, the mobile station can calculate a block error rate, so that outer loop power control can be performed even when receiving TF0.
The reason why the transport block of 0 bit is transmitted instead of becoming DTX when there is no control information (DCCH) to be transmitted is that the mobile station performs outer loop power control to keep receive quality of the A-DPCH to be a predetermined target quality in both cases of TF0 and TF1. The receive quality is BLER of DCH, SIR of TPC command and dedicated pilot in DPCCH, and the like.
There is a difference of about 1.5 dB˜2.0 dB in a required SIR per 1 symbol between a case in which transmission is performed using TF0 of table 4 and a case in which transmission is performed using TF1 of table 4. That is, the required SIR per 1 symbol is smaller by about 1.5˜2.0 dB in the case in which transmission is performed using TF0 compared with the case in which transmission is performed using TF1.
By the way, the control information DCCH is control information for performing report on, for example, Active Set Update, Measurement control, Physical channel reconfiguration and the like, and the transmission occurrence frequency is small. In other words, in most time, transmission is performed using TF0 in the table 4, and transmission using the TF1 in the table 4 is performed once in a while.
On the other hand, as mentioned above, when receiving more than one TF, the mobile station performs inner loop power control and outer loop power control without distinguishing the difference of the more than one TF. That is, as to A-DPCH, the mobile station performs inner loop power control and outer loop power control without distinguishing the difference of TFs when the radio base station performs transmission using the TF0 in the table 4 and also when the radio base station performs transmission using the TF1 in the table 4.
On the basis of the above-mentioned facts, since transmission is mainly performed using TF0 shown in the table 4 in A-DPCH, the target SIR of inner loop power control in the mobile station converges with respect to TF0 in the table 4. In this case, the target quality is smaller than required SIR as for TF1 in the table 4. As a result, as to TF1, a predetermined QoS (DCH quality target) cannot be satisfied.
For the above-mentioned problem, when the radio base station transmits TF1, it may be considered to increase transmission power compared with the case for transmitting TF0, for example. However, by such a method, since complexity of apparatuses implemented for all of many radio base stations becomes very large, that is not a realistic solving measure.
[Non-patent document 1] 3GPP TR34.108v5.3.0
[Non-patent document 2] 3GPP TR25.211v5.6.0
[Non-patent document 3] 3GPP TR25.214v5.9.0